Refrigeration systems are sometimes used to provide ultra-cold conditions for various applications. Refrigeration system parameters are generally designed for efficient operation under normal operating conditions, where the refrigeration system removes only ambient heat gain from the temperature controlled space to maintain temperature. Such systems do not adequately meet the greater cooling demands encountered on initial cool down of the controlled space, or during periods of increased access. In a typical compressive, two-stage cascade ultra-low temperature refrigeration system cooling capacity is determined primarily by the flow rate of the refrigerant through the expansion or flow control devices when the system compressors are operating.